1. Field of the Invention
The present invention relates to organic light emitting devices, and more particularly to white organic light emitting devices in which hosts having different properties are mixed in a light emitting layer, which provides a white organic light emitting device with reduced driving voltage and enhanced color stability even under high luminance conditions.
2. Discussion of the Related Art
In recent years, the field of displays that visually express electric information signals has rapidly developed with the advent of the information age. Correspondingly, a variety of flat display devices having excellent performance, such as slim design, low weight and low power consumption, have been developed and replaced rapidly conventional Cathode Ray Tubes (CRTs). (PDP), Field Emission Display (FED), and Organic Light Emitting Device (OLED).
Among the aforementioned ones, the OLED has competitiveness because it does not need a separate light source and realizes a compact device design and accurate color reproduction.
In the case of the OLED, formation of an organic light emitting layer may be necessary.
The proposed OLED is configured such that the organic light emitting layer is not patterned per pixel and stacks including different colors of organic light emitting layers are stacked one above another to display white light.
More specifically, in a white organic light emitting display device, respective layers between a cathode and an anode are deposited one above another without a mask upon formation of a light emitting diode. In other words, organic films including organic light emitting layers are sequentially formed using different material components and are deposited under vacuum.
The white organic light emitting display device is a multipurpose device, which is usable in, for example, a full-color display device including a thin light source, an LCD backlight, or a color filter.
A conventional white organic light emitting display device is configured such that stacks emitting different colors of light respectively include hole transfer layers, light emitting layers and electron transfer layers.
Each light emitting layer includes a single host and a dopant having the same color as light to be emitted, and is adapted to emit a corresponding color of light via recombination of electrons and holes introduced into the light emitting layer.
However, the above-described conventional white organic light emitting device has the following problems.
In the case in which the light emitting layer containing the single host and the dopant is designed, the light emitting layer has a narrow energy band-gap and causes leakage of electrons and holes into the electron transfer layer and the hole transfer layer, which prevents generation of excitons in the light emitting layer or increases leakage possibility of excitons generated via recombination. This results in deterioration in excitation efficiency caused by electron/hole recombination.